Recently, miniaturization, weight lightening and higher performance of portable electronic devices such as a laptop, PDA, MP3 and a cellular phone are in progress. Accordingly, a secondary battery having a high capacity and high stability is required for a power supply of a portable electronic device. As a secondary battery suiting the purpose, a nickel-cadmium storage battery has been used, and a nickel-hydrogen storage battery as a battery having higher energy density, and a lithium secondary battery as a non-aqueous electrolyte secondary battery have been commercialized.
As a positive electrode active material used in a commercialized lithium secondary battery, LiCoO2 may be mentioned, and a lot of research on replacing it with LiNiO2, LiMnO4, V2O5, etc. has been recently conducted, but there was a limitation of low energy density. Therefore, research on an electrode material having high theoretical energy density is needed for developing a battery having high energy density. According to recent research, it was reported that a lithium/sulfur battery has high theoretical energy density of 2600 Wh/kg at room temperature. In addition, sulfur is an abundant resource, and cheaper than other electrode materials.
When the electrode is designed to be thick for manufacturing a battery having high energy density, potential unbalance in the electrode may occur, and thus, it was difficult to manufacture a thick electrode. Accordingly, the battery was mostly manufactured by stacking multiple layers of thin electrodes, however, in this case, the weight of the electrode was increased due to the multiple layers of metal current collectors, thereby making it difficult to increase energy density.
Therefore, the need for an electrode having a light weight while being thick to have sufficient energy density was increased.